[time-nuts] Antique Rubidium Standard Questions

[paul swed]

When all else fails check the grounds. Especially 40 year old screws.

On Tue, Apr 24, 2012 at 6:13 PM, ed breya <eb at telight.com> wrote:

> Ed,
>
> Tuning the cavity should peak everything - it just maximizes the
> excitation power at the microwave frequency, so you get the most output
> from the Rb light wavelengths. A mechanical cavity resonator will have a
> very wide (compared to the modulation frequencies you're looking for)
> bandwidth, so unless something happened to it physically, it should be OK
> as originally built or adjusted. However, you may want to look at the
> multiplier chain and SRD bias circuit components and adjustments - those
> could have drifted quite a bit over forty years, limiting the microwave
> power due to being off-frequency, or having poor multiplication efficiency.
>
> I'm guessing that the second harmonic is indeed present, but just buried
> in the noise, and the loop still can "lock" because of the further signal
> processing, even though you don't see the evidence - remember it's a
> lock-in amplifier capable of digging a tiny signal out of the noise. If you
> go through the multiplier and check and tweak things, you may get more
> excitation power and signs that it's getting back to normal. Once you get
> enough power, if the Rb cells are still good, the second harmonic signal
> should show up large enough for the circuit to detect sufficient S/N ratio
> and provide a valid lock indication.
>
> Ed Breya
>
>
> Ed Palmer wrote:
>
> Could the drift be at least partially responsible for the lack of second
> harmonic?  A message on the list (
> <http://www.febo.com/**pipermail/time-nuts/2006-**April/020562.html<http://www.febo.com/pipermail/time-nuts/2006-April/020562.html>
> >http://www.**febo.com/pipermail/time-nuts/**2006-April/020562.html<http://www.febo.com/pipermail/time-nuts/2006-April/020562.html>) said
> that you could peak the second harmonic by adjusting the cavity tuning.
> If the cell and the cavity are out of sync would that kill the second
> harmonic?  How close to they have to be?  If this thing has a cavity
> tuning adjustment I haven't found it.
>
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